The present invention relates to an apparatus for coating a conveyed long, flexible support (hereinafter referred to as "a web" when applicable) with a liquid-type coating compound.
An example of a coating apparatus which has been extensively employed to coat a liquid-type coating compound (hereinafter referred to as "a coating liquid" when applicable) onto a web is multi-layer slide bead coating apparatus as proposed in U.S. Pat. No. 2,761,791 issued to Russell et al. In this conventional coating apparatus, a plurality of coating liquids flow down the slide surface striking against a conveyed web at the lower end of the slide surface so as to form a bead. By utilizing the bead, the coating liquids are applied to the web. Accordingly, in a coating apparatus of this type, it is essential to maintain the bead stable in order to successfully apply the coating liquids to the web. However, as the coating speed is increased, it tends to become difficult to maintain the bead stable.
In order to overcome this difficulty, an improved coating apparatus was proposed by Jackson in U.S. Pat. No. 3,928,678. This coating apparatus can eliminate the instability of the bead which results as the coating speed is increased. In the conventional coating apparatus, a lip-shaped member is provided at the lower edge of the slide surface for decreasing the speed of the layer of coating liquid flowing down the slide surface in order to increase the thickness of the liquid flow and to thereby to make the bead stable. With such a coating apparatus, particle effect in the coating liquid (appearance of stripes due to irregular coating) is observed which may be attributed to the increase of the thickness of the layer of coating liquid. However, if it is desired to increase the coating speed with the bead maintained stable, this coating apparatus is not suitable. That is, the permissible increase in coating speed is not more than about 10%. In addition, the increase is permitted only in the case where the flow rate of coating liquid is relatively high. If the flow rate of coating liquid is relatively low, the permissible increase is sometimes lower than that of the coating apparatus proposed by Russell et al U.S. Pat. No. 2,761,791.
Accordingly, an object of this invention is to provide a coating apparatus in which all of the above-described difficulties accompanying a conventional coating apparatus have been eliminated and the coating speed can be greatly increased especially in the case where the flow rate of coating liquid is a relatively low rate.